This application is based on Japanese Patent Application 2002-009785 filed on Jan. 18, 2002, the entire contents of which are incorporated herein by reference.
(1) Field of the Invention
This invention relates to a semiconductor device production method and semiconductor device production apparatus and, more particularly, to a semiconductor device production method and semiconductor device production apparatus for performing a cleaning process to reduce metal oxides produced on metal which forms electrodes or wirings on a semiconductor device.
(2) Description of the Related Art
Conventionally, aluminum has widely been used as material for electrodes and wirings on semiconductor devices. However, in recent years demands for minute semiconductor devices and high-speed processing have made it difficult to form electrodes and wirings with aluminum. For this reason attempts to use copper, which can withstand electro-migration and the resistivity value of which is small, as next generation material which replaces aluminum are being made.
If copper is used as material for electrodes and wirings, then electrodes and wirings will be formed by a damascene method because it is hard to etch copper. In this case, minute semiconductor devices and high-speed processing can be realized by increasing the aspect ratios of electrodes and wirings formed.
By the way, copper used in this way as material for electrodes and wirings is oxidized easily. When semiconductor devices are in the process of being manufactured, a copper oxide, such as cupric oxide (CuO) or cuprous oxide (Cu2O), may be produced on copper formed on them as electrodes and wirings. These copper oxides will cause, for example, an increase in electrical resistance, resulting in degradation in the characteristics of semiconductor devices. Therefore, a cleaning process for eliminating copper oxides which have been produced is performed after electrodes or wirings are formed.
Methods performed in a vapor or liquid phase have been discussed or put to practical use as the process of cleaning electrodes or wirings. In the process for manufacturing semiconductor devices, this cleaning process is performed as a process after a chemical mechanical polishing (CMP) process performed after lower layer wirings of copper being formed. This cleaning process is also performed as a process after a CMP process performed after copper being embedded in via holes for buried electrodes formed in an insulating layer, which lead to lower layer wirings, or trenches for wirings formed in the insulating layer. In some cases, this cleaning process is performed as a process before a physical vapor deposition (PVD) or chemical vapor deposition (CVD) process performed on via holes or trenches.
If a cleaning process is performed as a process after a CMP process, usually particles are eliminated with a brush scrubber and copper oxides produced on an insulating layer and copper oxides produced on copper embedded in via holes or trenches are eliminated with a chemical. In this case, a chemical which eliminates copper oxides and which has a weak etching action on metal copper will be selected. For example, carboxylic acid, such as citric acid (C3H4(OH)(COOH)3) or oxalic acid ((COOH)2), hydrofluoric acid (HF), or the like will be used as a chemical.
If a cleaning process is performed as a process before a PVD process, then the cleaning process will be performed before barrier metal being deposited by PVD in via holes leading to lower layer wirings. Then copper seeds are deposited by PVD in the via holes where the barrier metal has been deposited. Copper is embedded on the copper seeds in the via holes by plating. As a result, buried electrodes which connect with lower layer wirings are formed. That is to say, a cleaning process at this stage will improve electrical reliability between lower layer wirings and copper, which forms buried electrodes, via barrier metal.
If a cleaning process is performed as a process before a CVD process, then the cleaning process will be performed after a CMP process, which is performed after copper being embedded in via holes for buried electrodes, and before a silicon nitride (SiN) film or the like of several-hundred-nanometer thickness being formed by CVD. This silicon nitride film formed prevents copper from diffusing from lower layer wirings or buried electrodes into an insulating layer and prevents the copper from oxidizing.
If a cleaning process is performed in this way as a process before a PVD or CVD process, argon sputtering is often used to perform the cleaning process.
Moreover, Japanese Patent Laid-Open Publication No. 2001-271192 discloses the method of eliminating copper oxides by causing water vapor or acetic acid to act on them.
Furthermore, Japanese Patent Laid-Open Publication No. 2001-254178 discloses the method of eliminating a metal film which has adhered to the process chamber of, for example, a CVD system by causing cleaning gas which contains carboxylic acid or its derivative to act on it and by making the metal complexes.
However, the following problems arose as to conventional cleaning processes.
With a cleaning process performed as a process after a CMP process, particles are eliminated and copper oxides are eliminated with a chemical. Then cleaning with deionized water is performed to eliminate a residual chemical. In this cleaning with deionized water, however, with a gradual elimination of a chemical, acid cleaning water becomes neutral and its pH value becomes greater. As a result, copper which forms buried electrodes and wirings is corroded.
If the concentration of a chemical is high and the pH value of cleaning water is small, then the exposed surfaces of buried electrodes and wirings are corroded slightly. However, if the concentration of a chemical is low and the pH value of cleaning water is great, then copper which forms buried electrodes and wirings is corroded locally and their surfaces become irregular. It therefore is difficult to keep the exposed surfaces of buried electrodes and wirings flat.
With a cleaning process performed as a process before a PVD process, a physical elimination method using argon sputtering enables a process in a vapor phase without using a chemical. However, contaminants once eliminated may adhere again to lower layer wirings which are exposed at the bottom of via holes formed so that they will lead to the lower layer wirings. Moreover, the edge portions of via holes are lost by sputtering, so minute buried electrodes cannot be formed.
With a cleaning process performed as a process before a CVD process, a shift from a CMP process to the CVD process needs a semiconductor device movement between process systems. As a result, copper which forms wirings is exposed to the air and there is a strong possibility that copper is oxidized.
Therefore, in this case, plasma treatment with reducing gas, such as hydrogen (H2) or ammonia (NH3), is performed as pretreatment in a CVD system before a silicon nitride film is formed by CVD. However, this plasma treatment must be performed in a high-temperature environment (at a temperature of about 400xc2x0 C.). Therefore, exposed copper recrystallizes due to heat and a copper surface may become irregular. When after that an insulating material, such as a silicon nitride, is deposited, a coating of the insulating material deteriorates locally.
With a conventional cleaning process using gaseous acetic acid, copper oxides can be eliminated by a vapor phase reaction without using a chemical. However, another process with water vapor must be performed to eliminate contaminants, such as carbonaceous ones, which will remain on a copper surface after a cleaning process. As a result, a treatment process becomes complex.
The present invention was made under the background circumstances as described above. An object of the present invention is to provide a semiconductor device production method and semiconductor device production apparatus for performing a cleaning process by uniformly and efficiently reducing metal oxides produced on metal which forms electrodes or wirings on a semiconductor device.
In order to achieve the above object, a semiconductor device production method for performing a cleaning process to reduce metal oxides produced on metal which forms electrodes or wirings on a semiconductor device is provided. This semiconductor device production method comprises the step of performing a vapor phase cleaning process to reduce the metal oxides to metal and produce gaseous carbon dioxide and water by introducing gaseous carboxylic acid into a process chamber in which the semiconductor device is located.
Moreover, in order to achieve the above object, a semiconductor device production apparatus for performing a cleaning process to reduce metal oxides produced on metal which forms electrodes or wirings on a semiconductor device is provided. This semiconductor device production apparatus comprises a process chamber including a process table on which the semiconductor device is placed and a heater located beneath the process table for heating the semiconductor device, a storage tank for storing carboxylic acid which reduces the metal oxides, a treating gas feed pipe located between the process chamber and the storage tank, and a carburetor located along the treating gas feed pipe for vaporizing carboxylic acid which flows through the treating gas feed pipe from the storage tank to the process chamber.
The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.